Usage of radio spectrum, or spectrum for short, is regulated independently within different countries, or regions. An authority regulating spectrum usage in a certain region may be referred to as a regulator. Radio communication systems, such as cellular telecommunication systems, are developed and designed for different spectrum ranges, or operating bands. An operating band may be referred to as an operating frequency band.
An operating frequency band supports a specific duplex mode of operation. The possible duplex modes are frequency division duplex (FDD), time division duplex (TDD) and half duplex FDD (HD-FDD). In FDD mode of operation, which is used in Universal Terrestrial Radio Access Networks (UTRAN) FDD and Evolved Universal Terrestrial Radio Access Networks (E-UTRAN) FDD, the uplink and downlink transmission take place on different carrier frequencies. Reference is made to Third Generation Partnership Project (3GPP) TS 25.101, “User Equipment (UE) radio transmission and reception (FDD)”, 3GPP TS 25.104, “Base station (BS) radio transmission and reception (FDD)”, and 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception” and 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception”. Therefore, in FDD mode both uplink and downlink transmission can occur simultaneously in time. The carrier frequencies used in the uplink and the downlink are referred to as pass band for uplink and downlink, respectively. The minimum distance in frequency between the uplink and downlink pass bands is referred to as a duplex gap. The distance in frequency between the uplink and downlink carrier frequencies is referred to transmit-receive (TX-RX) frequency separation for the radio transmitter. The TX-RX frequency separation can be fixed, aka default, or variable. In the latter case the TX-RX frequency separation is configurable by the network.
On the other hand in TDD mode, which is used in UTRAN TDD and E-UTRAN TDD, the uplink and downlink transmission take place on the same carrier frequency channel but in different time slots or sub-frames. Reference is made to 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception”, 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception” and 3GPP TS 05.05, “Radio Transmission and Reception”.
HD-FDD, which is used in Global System for Mobile Communications (GSM), can be regarded as a hybrid scheme where the uplink and downlink are transmitted on different carrier frequencies and are also transmitted on different time slots. Reference is made to 3GPP TS 05.05, “Radio Transmission and Reception”. This means uplink and downlink transmission do not occur simultaneously in time.
Returning to spectrum usage, one of the objectives of standardizing spectrum usage is to develop an operating band which can, preferably, be used globally. A global operating band leads to several advantages in terms of global roaming, reduced cost of the products due to the economy of scale, simplicity in building products/devices since the same, or at least at limited number of, platforms/devices can be reused globally or regionally etc. For each platform, a lot of research and development is required. Thus, a large number of platforms increase cost. However, certain region specific and even operator specific frequency bands are unavoidable due to the fact that the spectrum availability for mobile services may be fragmented in different countries and even within a country. The mobile services are typically operated by the cellular telecommunication systems. Furthermore, the regulators in each country independently allocate the frequency band in accordance with the available spectrum.
The spectrum below 1 GHz, might be scarce or fragmented due to higher demand by other competing technologies due to its favorable propagation characteristics. The assigned spectrum is eventually standardized in 3GPP in terms of frequency bands so that vendors can develop products, such as base stations and user equipments. Expressed differently, the standardized frequency band is written into 3GPP specifications. Hence, there may be a frequency band that is completely allocated in one region while a different region just allocates part of it. For example, Band 5 is widely used. However, only a sub-band of it is used in Region B, which is called Band 19. Band 5 and band 19 are known from 3GPP terminology. FIG. 1 shows a block diagram illustrating a frequency arrangement for band 5 and band 19. The numbers at the ends of each rectangle indicate frequency in MHz and the arrows in each rectangle indicate uplink for an arrow pointing upwards, and downlink for an arrow pointing downwards. The meaning of the arrows applies to FIG. 2 below as well.
One more example of a scarce or fragmented spectrum portion is that of the frequency allocation in the range of 700 MHz, i.e. 700-799 MHz. In the range of 700 MHz, there is potential for a new frequency band Asia Pacific region (APAC). Related to this new frequency band, it is desired to harmonize the use of a band in the range of 798-806 MHz. This band has previously been used mainly for TV broadcasting. The regulatory work is managed by APT (Asia Pacific Telecommunity) Wireless Group (AWG). Since the agreements made in the AWG are not legally binding for member states of the AWG, each individual country may still implement their own band arrangement.
One arrangement for the band is to use 703-748 MHz in uplink and 758-803 MHz in downlink when using FDD. There is also a TDD allocation for the band covering 698-806 MHz.
APAC is a large region and therefore it is difficult to have the same spectrum allocation in all countries in the region. Thus, in some countries it is expected that the allocation may be a subset of the full band of 798-806 MHz, and in some countries it is expected that the allocation may be the full spectrum of 798-806 MHz. For example, some region (e.g. region B) may allocate only parts of the band for communication according to International Mobile Telecommunications (IMT). As an example, the uplink may be placed in 715-750 MHz and the downlink in 770-805 MHz in region B. FIG. 2 shows another block diagram illustrating the frequency arrangements relating to the 700 MHz band for AWG, say region A, and region B.
The standardization of a frequency band encompasses various aspects including the band numbering, raster, carrier frequency channel numbering, radio requirements for user equipments and base stations, performance requirements for user equipments and base stations, radio resource management (RRM) requirements etc. Some or all of these factors have to be taken into account by a manufacturer of for example user equipments and radio base stations. Examples of radio requirement for user equipments are requirement concerning out of band emission, radio frequency (RF) exposure to human and more.
In the following a few known examples relating to handling of radio requirements, or radio emission requirements, are presented.
Although a wireless device typically operates in a well defined portion of the frequency band, emissions outside its operating or channel bandwidth and also outside its operating frequency band are unavoidable. These emissions outside the band width, or frequency band, are often termed as out of band emissions (OOB) or unwanted emissions. The emissions both inside and outside the band width and/or frequency band of operation are also exposed to human body.
These two concepts, i.e. OOB emission and RF exposure to human, and their associated signaling aspects are described below.
Firstly, out of Band (OOB) Emissions are described. The user equipments as well as base stations have to fulfill a specified set of out of band (OOB) and spurious emission requirements. The Out of band emissions are unwanted emissions immediately outside the assigned channel bandwidth resulting from the modulation process and non-linearity in the transmitter but excluding spurious emissions. Spurious emissions are emissions which are caused by unwanted transmitter effects such as harmonics emission, parasitic emissions, inter-modulation products and frequency conversion products, but exclude out of band emissions. The objective of OOB emission requirements is to limit the interference caused by the transmitters (UE or BS) outside their respective channel bandwidths to the adjacent carriers due to for example non-linearity and component imperfections. In fact, all wireless communication standards, such as GSM, UTRAN, E-UTRAN, Wireless Local Area Network (WLAN) etc, clearly specify the OOB emission requirements to limit or at least minimize the unwanted emissions. Reference is made to 3GPP TS 25.101, “User Equipment (UE) radio transmission and reception (FDD)”, 3GPP TS 25.104, “Base station (BS) radio transmission and reception (FDD)”, 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception”, 3GPP TS 36.104, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); Base station (BS) radio transmission and reception” and 3GPP TS 05.05, “Radio Transmission and Reception”. Spurious emissions requirements are defined in order to limit the emissions out of the operating band where the UE or BS is operating due to for example harmonic emissions and inter-modulation products. They are primarily approved and set by the national and international regulatory bodies, e.g. International Telecommunications Union Radiocommunication Sector (ITU-R), Federal Communications Commission (FCC), Association of Radio Industries and Business (ARIB), European Telecommunication Standard Institute (MI), etc.
Some major OOB and spurious emission requirements, which are typically specified by the standards bodies and eventually enforced by the regulators in different countries and regions for both UE and the base stations comprise:                Adjacent Channel Leakage Ratio (ACLR)        Spectrum Emission Mask (SEM)        Spurious emissions        
The specific definition and the specified level of these requirements can vary from one system to another. Typically these requirements ensure that the emission levels outside the transmitter channel bandwidth or operating band remain several tens of dB below the transmitted signal. Emission levels tend to decay dramatically further away from an operating band but they are not completely eliminated at least in the adjacent carrier frequencies.
In order to handle, or control, unwanted radio emission, or OOB, a concept of maximum power reduction (MPR) is used in many telecommunication systems.
As stated above, the user equipment and the base station have to meet the OOB and spurious emission requirements irrespective of their transmission power level. For the UE the conservation of its battery power is very critical. This requires that the UE has an efficient power amplifier (PA). The PA is therefore typically designed for certain typical operating points or configurations or set of parameter settings e.g. modulation type, number of active physical channels, e.g. resource blocks in E-UTRA or number of CDMA (Code Division Multiple Access) channelization codes code/spreading factor in UTRA. But in practice the user equipment may operate using any combination of modulation, physical channels etc. Therefore, in some UL transmission scenarios the UE power amplifier may not be able to operate in the linear zone, thereby causing unwanted emissions due to harmonics or other non-linear characteristics. To ensure that UE fulfils OOB/spurious requirements for all allowed UL transmission configurations the UE is allowed to reduce its maximum UL transmission power in some scenarios when it reaches its maximum power. This is called maximum power reduction or UE power back-off in some literature. For instance a UE with maximum transmit power of 24 dBm power class may reduce its maximum power from 24 dBm to 23 or 22 dBm depending upon the configuration.
The base station (BS) may also have to perform MPR but this is not standardized. Secondly the BS can afford to have a PA with larger operating range since its efficiency is less critical compared to that of UE. The reason is that an inefficient PA leads to increase in power consumption decreasing the battery life. The UE power consumption due to its limited battery life is more critical compared to that of the BS.
The MPR values for different configurations are generally well specified in the standard. The UE uses these values to apply MPR when the conditions for the corresponding configurations are fulfilled. These MPR values are regarded as static in a sense that they are independent of resource block allocation and other deployment aspects.
Another concept is the so called additional maximum power reduction (A-MPR). In E-UTRA an additional MPR (A-MPR) for the UE transmitter has also been specified in addition to the normal MPR. The difference is that the former is not fully static. Instead the A-MPR can vary between different cells, operating frequency bands and more specifically between cells deployed in different location areas or regions. In particular the A-MPR may be applied by the UE in order to meet the so-called additional spurious emission requirements imposed by the regional regulatory organization. The user equipment is not allowed to reduce its maximum output power beyond the A-MPR. Therefore it is often termed as ‘allowed A-MPR’. However a typical user equipment implementation will apply the full allowed A-MPR in order to meet the additional radio emission requirements using RF power amplifier which leads to efficient utilization of its battery.
The A-MPR includes all the remaining UE maximum output power reduction, on top of the normal MPR, needed to account for factors such as: bandwidth, frequency band, resource block allocation, requirements set by regional regulatory bodies (FCC, ARIB, European regulation etc).
Furthermore, signaling of regulatory requirements and A-MPR to the UE is performed as follows. The regulatory requirements may vary from one region to another and from one network to another. The presence of additional regulatory requirements is signaled via a cell specific signaling known as network signaling (NS). Reference is made to 3GPP TS 36.101, “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access (E-UTRAN); User Equipment (UE) radio transmission and reception”. Associated with the NS signaling there is a set of A-MPR which may depend on for example resource block allocation.
To meet the regulatory emission requirements the A-MPR required could vary from one part of the network to another. This is due to the factors such as the variable bandwidth, varying number of resource block allocation, different bands in different parts of the networks etc. Even if the deployment scenario, in terms of bands used, bandwidth size etc., is homogeneous in a large coverage area, there will always be border regions between these coverage areas. Therefore A-MPR is a cell specific value.
Due to the above reasons the A-MPR is signaled to the UE via system information in a UE specific channel or in a broadcast message. This allows the UE to acquire this information when it camps on to a cell. The acquired A-MPR value which is associated with a cell is then used by the UE to reduce its maximum output power whenever it transmits in the uplink.
Secondly, the concept of handling, or controlling, RF Exposure to Human is described. Another important factor, apart from OOB, is the human exposure to radiofrequency (RF) electromagnetic fields (EMF), which are transmitted by the UE. The most important guidelines on RF exposure to human are from the International Commission on Non-Ionizing Radiation Protection (ICNIRP, 1998) and from the Institute of Electrical and Electronics Engineers (IEEE, 1999). The limits in these recommendations are similar and they have been used as the basis for national standards and regulations in many countries. The ICNIRP guidelines, which are the most widely used recommendations, have been endorsed by the World Health Organization (WHO).
These RF exposure guidelines are science-based and the prescribed limits have been set with substantial safety margins. They provide protection from all established health effects from short-term and long-term exposure to RF fields, and the safety of children and other segments of the population have been taken into account.
Specific Absorption Rate (SAR) is introduced to measure impact on the human body from the exposure of RF EMF transmitted by the UE. SAR is a measure of the maximum energy absorbed by a unit of mass of exposed tissue of a person using a mobile phone, over a given time or more simply the power absorbed per unit mass. Advised by ICNIRP, the communication administration departments of different countries issued the SAR limits. For instance, the Federal Communications Commission (FCC) has determined that the SAR limit is 1.6 W/kg for cell phone. The SAR limit in Europe and in most of countries is 2 W/kg.
A reduction of power limits RF exposure to human. Thus, the user equipment should comply with the SAR requirements or any type requirements for limiting the RF exposure to human which are specified by the regulator in an individual country, region, province or state etc. In order to meet these requirements the user equipment may also have to reduce its maximum output power. Hence, the user equipment maximum output power is limited by the SAR limit.
In prior art, a generic term called power management is also interchangeably used for controlling emissions to limit the SAR. The power management MPR (P-MPR) is the amount of UE power output power reduction to meet the RF exposure requirements.
Now, a known concept of signaling of RF Exposure Requirements to the user equipment is described. One or more parameters associated with the MPR to be applied by the user equipment to meet the SAR or any type of RF exposure requirements are signaled to the user equipment. This means the P-MPR may also be signaled to the user equipment. This is due to the fact that SAR or RF exposure requirements may vary from one region to another. Hence the amount of the MPR required by the user equipment to meet the requirements may vary from one cell to another.
When developing and designing a user equipment, an aspect that often is thoroughly considered is cost of the user equipment. Cost of the user equipment is for example dependent on number of duplexers, or duplex filters, comprised in the user equipment. A duplexer is used to connect a transmitter and a receiver to an antenna. The user equipment comprises the transmitter, the receiver and the antenna. The duplexer is designed to prevent interfering signals transmitted by the transmitter from reaching the receiver. Interference from the transmitter to the receiver is commonly referred to as transmitter noise. One source of transmitter noise is called transmit inter-modulation (IM) products. It shall be noted that IM is a type of OOB emission. Thus, the duplexer should also be designed to substantially suppress transmitter noise.
The design and implementation of a duplexer becomes more difficult depending upon various factors. Notably, if a pass band is wide and if a duplex gap of the band is small, attenuation requirements in stop-band becomes large. The attenuation requirements relates to requirements for OOB, RF exposure and the like. The stop-band defines a frequency range in which reduced, or at least less than some threshold value, transmission from the transmitter is desired. As an example, an attenuation requirement may be a threshold level for OOB. In case of FDD 700 MHz, with full spectrum allocation, the pass band is very wide, i.e. 45 MHz in each direction, and the duplex gap is small. Presently, it is suggested that a user equipment configured for operation in such operating frequency band will use two duplexers. As a result, the attenuation requirements are believed to be fulfilled.
As mentioned above, a frequency band in the range of for example 700 MHz may have full spectrum allocation in certain regions, which herein are referred to as region A. On the other hand in some other regions, the spectrum allocation may be subset of the full band. Such regions are referred to as region B herein. Therefore, an issue is how to handle spectrum allocation in different regions.
To address the above mentioned issue, a first solution is to define one frequency band based on the largest or full allocation. This approach simplifies roaming and ensures the economy of scale, i.e. there is no need for devices designed, or configured, for specific regions. However, due to large allocation in full band, e.g. FDD UUDL: 2×45 MHz with 10 MHz duplex gap, the user equipment will require two duplex filters to cover the entire band as mentioned above. This will increase the cost for user equipments in regions where it would be sufficient to have single duplexer in the user equipment due to partial allocation of the band. That is, cost of user equipments operating in region B will be unnecessarily high.
Therefore, in order to reduce cost of the user equipment operating mainly in region B, two bands are defined according to a second solution. A first band “band Y” covers the entire frequency range, or the full spectrum, and a second band “band X” covers a subset of the full spectrum. Advantageously, cost of user equipments configured for region B may be kept lower since only one duplexer is needed. FIG. 3 shows a further block diagram illustrating another exemplifying frequency arrangement for the first band “band X”, applied in region A, and the second band “band Y”, applied in region B. In this general example, band X is an allocation to the full spectrum, or full band, and band Y is a partial allocation of the full spectrum. In this manner, multiple bands for overlapping frequency regions, or ranges, are defined.
For user equipments configured for a region where the full spectrum is allocated, such region is referred to as region A, the following disadvantage merges. In region B, radio emission of a user equipment configured for region A may not be accurately controlled since out of band emission and the like may differ between the user equipment configured for region A and a user equipment configured for region B.
The first and second solutions above become even more problematic in case the frequency band is significantly large with smaller duplex gap. In this case, the first solution may require even more than two duplexers to cover the entire band. In the second solution, more than two bands, e.g. band X, band Y, band Z etc, may have to be defined.